Computer users have the ability to add color to their documents using popular application software for desktop publishing, spreadsheets, forms, etc. As used herein, the term document refers to a visual display of a graphical image, whether on a CRT or on paper, and the digital data required to generate the visual display is called a document file. Typically, if a user wishes to print a color document, the document file is sent to a process color printing system. Process color is defined as the mixing of toners to obtain a particular hue and saturation of a given color. Process color printing systems commonly use cyan, magenta, yellow and black toners to create colors. Various combinations of color toners are mixed or overlaid to create a desired color. A process color printer generally makes four (4) passes to print a color document, one pass for each of the process color toners available in the printer. When a color document is sent to a process color printing system, the colors seen on the display when viewing the document are similar to the colors on the printed output.
Accent color is becoming commonplace in today's business environment. A significant volume of color work can satisfactorily and economically be accomplished by accent color printers. Accent color is defined as using the toners installed in an accent color printer to represent a process color without any mixing or overlaying of toners. Shades of a color are depicted using a percentage of a particular toner. Some printers that do accent color printing also do shading by creating patterns with a combination of black plus a color toner to produce different shades of a particular color without actually placing one color of toner on top of another color of toner. Document preparers use accent color for a variety of purposes, including logos, signatures, forms, highlighting key topics of a document, emphasis on variable data and personalized information. Because an accent color printer may require fewer passes to print an accent color document, accent color printing can be faster and less expensive than process color printing. If a document has only black, red and blue, three (3) passes are required versus four (4) passes for a four color process color printer. Since the tolerances for color registration in an accent color marking engine can be less than for a process color marking engine, an accent color marking engine can be manufactured less expensively than a process color marking engine.
A current challenge with printing color documents on an accent color printer is how to change a process color specification, which typically requires four toners, to an accent color specification using fewer than four color toners. Another challenge is how to represent colors that are darker than a pure color that is normally represented by 100% of a toner. When generating business graphics or documents, a document preparer is concerned with highlighting information using color but is not necessarily as concerned with matching a particular color.
An example of a printer that is designed to print accent color is the Xerox 4890, manufactured by Xerox Corp., Rochester, N.Y. The Xerox 4890 prints black plus one accent color. To process accent color documents, the Xerox 4890 employs a file server, called a FIBRE.TM. server, that is installed in front of the 4890 controller to convert a document file having process color data to a best accent color match. Commands are inserted by the file server into the document file to specify where accent color is to be used. If blue is available in the Xerox 4890 printer, all blue colors in the document are represented as a combination of black and blue toner, with all other colors represented as a shade of gray. The Xerox 4890 printer limits the user to only one accent color for a document.
It would be desirable to have a system that is capable of providing more than one accent color and which provides an efficient process for mapping process color commands to the toner colors available on the accent color printer. It would also be desirable to have such a system that would produce aesthetically pleasing results.